CNC (Computer Numerical Control) machine tools are the main machining equipments in mechanical machining field. Based on an ordinary machine tool, a Numerical control machine tool has an additional digital control function, which can improve the machining precision, improve the capacity of machining complex workpieces, do a quick response to change of the machined parts, and increase the production efficiency greatly. A numerical control system (NCS) is the control brain of the Numerical control machine tool. The NCS' quality directly affects the machining quality and the machining efficiency of the Numerical control machine tool. Storage is one of the core parts of NCS, and it has a great influence on the whole performance of NCS.
With the rapid development of semiconductor technology, storage is developing from low speed and small capacity to high speed and large capacity. Storage used in the NCS is generally divided into two categories: internal memory and flash memory. The internal memory is configured to store data and programs which are needed when the CPU is in operation. The internal memory has a great effect on the operation speed of the CPU. An internal memory with a high storage capacity can effectively increase the speed and stability of the system, while an internal memory with a low storage capacity will become a bottleneck affecting the performance of the whole system. Flash memory is a nonvolatile memory and doesn't lose data when power turns off. Flash memory is mainly used to store data for a long time.
As the main storage scheme many years ago, the storage scheme of SRAM+DDR+CF of the NCS has experienced the rapid development of semiconductor technology in recent years, and no longer has obvious technical advantages, but at the same time shortcomings begin to appear.
From read-write speed of a storage, storage capacity, price, market applications and other aspects, analysis is done as below:
SRAM: the mainstream capacity is 4 Mb, the read-write time is 45 ns. The development of SRAM technology is slow, and there is no qualitative leap in recent years. The disadvantage is that the capacity is small and the price is expensive.
DDR SDRAM: the mainstream capacity is 512 Mb, the maximum capacity is 1 Gb, the maximum frequency is 200 MHz. The development of DDR technology is rapid and it is developed from DDR to DDR2, DDR3. The speed of reading and writing has doubled, and the maximum frequency of DDR3 has reached 1066 MHz. The latest DDR4 technology has already been put into production.
CF card: the mainstream capacity is 4 GB and the maximum speed of reading and writing is 25 MB/s. CF cards have been completely replaced by SD cards in the field of digital products, but still occupied the mainstream position in the industrial control field. The disadvantage of CF card is expensive. The maximum read and write speed of a 4 GB SD card is 20 MB/s.
In addition, the storage scheme SRAM+DDR+CF having only removable CF card as saving system files and user data, the CNS cannot be used in the absence of CF card.
Therefore, it is desirable to provide a CNS and a Numerical control machine tool to solve the above problems.